Deck 20: Thermodynamics and Gas Properties

Question 1

Which of the following problems are posed by increasing the number of reheats?

A)cost & fabrication problems arise
B)heat transfer problems arise
C)frictional losses arise
D)none of the mentioned

Answer 1

cost & fabrication problems arise

Question 2

What is the most preferable dryness fraction of the exhaust steam?

A)0.99
B)0.77
C)0.66
D)0.88

Answer 2

0.88

Question 3

Which of the following represents the specific volume during phase transition.

A)vf-vg
B)vg-vf
C)vf+vg
D)none of the mentioned

Answer 3

vg-vf

Question 4

An 80 litre vessel contains 4 kg of R-134a at a pressure of 160 kPa. Determine the volume occupied by the vapour phase.

A)0.0775 m³
B)0.0575 m³
C)0.0975 m³
D)0.0375 m³

Question 5

Rankine cycle comprises of___________              

A)two isentropic processes and two constant volume processes
B)two isentropic processes and two constant pressure processes
C)two isothermal processes and two constant pressure processes
D)none of the mentioned

Question 6

In Rankine cycle, the work output from the turbine is given by___________              

A)change of internal energy between inlet and outlet
B)change of enthalpy between inlet and outlet
C)change of entropy between inlet and outlet
D)change of temperature between inlet and outlet

Question 7

Which of the following contributes to the improvement of efficiency of Rankine cycle in a Thermal Power Plant?

A)reheating of steam at intermediate stage
B)regeneration use of steam for heating boiler feed water
C)use of high pressures
D)all of the mentioned

Question 8

A simple Rankine cycle operates the Boiler at 3 MPa with an outlet temperature of 350°C and the Condenser at 50 kPa. Assuming ideal operation and processes, what is the thermal efficiency of this cycle?

A)7.7
B)17.7
C)27.7
D)37.7

Question 9

How many types of feedwater heaters are present?

A)one
B)two
C)three
D)four

Question 10

The temperature of feedwater leaving a heater is___________the saturation temperature at steam extraction pressure.

A)less than
B)equal to
C)more than
D)none of the mentioned

Question 11

The following also gave two-constant equations of state.

A)berthelot
B)dieterici
C)redlich-kwong
D)all of the mentioned

Question 12

Which of the following is true about compressibility of real gases?

A)z = 1
B)z < 1
C)z > 1
D)both z < 1 and z > 1 view answer

Question 13

1 mole of cyclohexane (z = 1.2) is filled in a container at 27°C and 4 atm, what is the volume of container?

A)3.8 liter
B)4.4 liter
C)5.6 liter
D)7.4 liter view answer

Question 14

If a relation exists among variables x,y,z then z may be expressed as a function of x and y as, dz=Mdx+Ndy .

Question 15

A pure substance which exists in a single phase has___________independent variables.

A)zero
B)one
C)two
D)three

Question 16

Which of the following is not a Maxwell equation?

A)(?t/?v) = -(?p/?s)
B)(?t/?p) = -(?v/?s)
C)(?p/?t) = (?s/?v)
D)(?v/?t) = -(?s/?p)

Question 17

The Clausius-Clapeyron equation is given by

A)dp/dt = l / t(vf+vi)
B)dp/dt = l / t(vf-vi)
C)dt/dp = l / t(vf+vi)
D)dt/dp = l / t(vf-vi)

Question 18

Water___________on melting and has the fusion curve with a___________slope.

A)contracts, negative
B)contracts, positive
C)expands, negative
D)expands, positive

Question 19

At the triple point, l(sublimation) = l(vaporization) - l(fusion).

Question 20

The slope of sublimation curve is___________the slope of the vaporization curve at triple point.

A)equal to
B)less than
C)greater than
D)none of the mentioned

Question 21

An application requires R-12 at ?140°C. The triple-point temperature is ?157°C. Find the pressure of the saturated vapour at the required condition.

A)0.0058 kpa
B)0.0098 kpa
C)0.0068 kpa
D)0.0088 kpa

Question 22

The expression which represents the pressure exerted by a gas is

A)nvrt
B)nrt/v
C)v/nrt
D)1/nvrt

Question 23

Which of the following relation is correct?

A)mole fraction of the kth gas = moles of the kth gas / total number of moles of gas
B)partial pressure of kth gas = (mole fraction of the kth gas)*(sum of the partial pressures)
C)sum of mole fractions of all the gases is unity
D)all of the mentioned

Question 24

The total entropy of a mixture of gases is the___________of the partial entropies.

A)average
B)weighted mean
C)sum
D)difference of the highest and the lowest

Question 25

When humidity ratio of air___________air is said to be dehumidified.

A)increases
B)decreases
C)remains constant
D)none of the mentioned

Question 26

The degree of saturation is the ratio of

A)(saturated specific humidity / actual specific humidity)^2
B)1/(saturated specific humidity * actual specific humidity)
C)saturated specific humidity / actual specific humidity
D)actual specific humidity / saturated specific humidity

Question 27

At any dbt, the___________the difference of wbt reading below below dbt,___________is the amount of water vapour held in mixture.

A)smaller, smaller
B)greater, greater
C)greater, smaller
D)smaller, greater

Question 28

When unsaturated air flows over a sheet of water in an insulated chamber

A)specific humidity of air decreases
B)the water evaporates
C)both air and water are cooled during evaporation
D)all of the mentioned